A linear variable differential transformer, commonly known as an LVDT, utilizes a magnetic core axially translating within an electromagnetic coil system consisting of primary and secondary coils to produce an electrical signal which may be interpreted for a variety of purposes. For instance, LVDT's are often utilized in the gaging and measuring arts to produce an electrical signal denoting location, size or dimension.
LVDT's and electrical gaging devices take a variety of forms, such as typically shown in U.S. Pat. Nos. 2,313,989; 2,365,592; 2,437,639; 2,583,791; 2,627,119 and 2,833,046. In conventional devices, a supporting member is commonly used to support the coil, and a sensing plunger or rod is axially translatable within the coil and includes a core within the coil which affects the electromagnetic characteristics of the coil as the core is displaced and positioned therein. For setup purposes adjustment means are employed for supporting the unit at a location adjacent to the article being engaged or measured. In current systems utilizing LVDT's for measurement purposes, the probe housing is normally moved in its entirety wherein the rod upon which the core is mounted contacts a reference surface and the coil and probe housing are physically positioned with respect to the core and reference surface to produce a null condition. Thus, the probe housing, or support, must be frequently released, repositioned, and reclamped, and it is an object of the invention to provide an LVDT probe which eliminates entire probe housing repositioning and which very quickly permits the core and coil to be relatively positioned in a predetermined relationship to produce the desired electrical characteristics.
Another object of the invention is to provide an LVDT probe utilizing a core and coil wherein alignment means are employed for positioning both the core and coil relative to each other and the probe housing and a reference surface to quickly achieve a predetermined electrical condition.
Yet another object of the invention is to provide an LVDT probe wherein both the core and coil are relatively movable to each other and to the probe housing, and a biasing force connection exists between the core and coil.
A further object of the invention is to provide an LVDT probe of simple and economical construction capable of being quickly adjusted to a null position, or other predetermined electrical condition, wherein the components are readily manufacturable at reasonable cost, and the probe is easily assembled.
In one embodiment of the invention a support member in the form of a tube having open ends includes at least one bearing in which a sensing rod is axially slidable. An LVDT core is fixed to this rod. An annular coil within the tube is disposed about the rod core and is supported for axial displacement relative to the tube and the core upon friction elements.
The probe rod extends from the end of its tube, and a spring coil interconnects the rod and the coil, or coil support, wherein the rod is biased relative to the coil and predetermined axial movement of the core rod produces axial displacement of the coil.
Initial positioning of the core rod and the coil is achieved by alignment means. In one embodiment such alignment means comprises a plunger slidable within a tube engagable with reference surfaces defined upon the core rod and coil, and in another embodiment the alignment means comprises a reference surface, such as a shim, engagable by the sensing end of the core rod and a tube affixed to the coil. In either instance, the desired predetermined axial relationship of the core and coil to each other is quickly achieved, and the apparatus is fabricated of components economically manufacturable and readily assembled.